I saw it today with DS7 and DS4. The 7-year-old was enthralled...we also teach our children about the circle of life, and also how we are a part of it on the top of the food chain (usually

). I absolutely loved it and will consider buying it for my son's first grade teacher & class when it comes out on DVD. Like one of the posters above, we teach real-life and nature rather than weapons and violence to our boys.
While there were scenes of predators catching prey, it was not graphic at all.
When a cheetah caught a gazelle after a long chase, it put it's paw onto the animal, and then the scene changed. You knew it was going to eat it, but there was no blood shown. Everything that you would expect in a nature documentary was implied, but never anything gory or particularly scary. Fascinating...definitely.
It is meant to be an educational movie about the earth/ecosystems/what we're doing to the planet, and especially about the cycle of life. The whole point of showing the father polar bear lying down to die is that the polar ice is melting so much earlier in the season due to global warming that he couldn't get to land before the pack ice melted. He ended up swimming for days to make it to shore, and then had no energy left to hunt. It is a true "reality show", not the junk that's on primetime. It also teaches the kids that the things we do every day, like leaving the lights on, has far-reaching impact on things like polar bears.
My 4-year-old liked most of it, but is too young to understand what the movie is really about. A few times he did inform the audience that he "hates the 'insert name of predator here'".
If you have younger children who are accustomed to the way nature works, they will not be scared by this movie.
If your kids are a bit more sheltered, wait until they start learning about the food chain in school and it won't be such a shock to them. It is rated G because there's absolutely nothing gory about it. Parts are definitely sad, but that's a part of learning about the cycle of life.
Can you tell I'm a bit passionate about this? I'll get down off of my soapbox now...